hi Rachel - one of the easiest ways to find out restrictions for countries is to visit the local site of one of the main courier companies such as UPS or Fedex etc as they will often have a help/FAQ section there on restricted or banned products for that country. You might also try the American Huel forum as they maybe more likely to have Hueligans on there who have knowledge.
If you’re flying then obviously check the airline too. They might have differences with what can go in carry-on and what can go in checked luggage.
I don’t think customs will class the seeds in Hot & Savoury as the same problem as people bringing in many bags of whole seeds. But definitely best to check with the country’s customs advice. Hopefully someone else has travelled to Costa Rica here though!